[LEAPSECS] POSIX and C (Was: Re: ISO Influence)

[Ian Batten]

On 23 Dec 2010, at 16:48, Warner Losh wrote:


> On 12/23/2010 02:49, Ian Batten wrote:

>> 

>>> Checking, I see that MSF transmits UTC but also encodes DUT1, so you can

>>> derive UK legal time by looking at bits 01B to 16B and *58B.

>> We used to do that for BT equipment, but they gave up, and now (so far as I know) all the UK telcos tick UTC(GPS).

> 

> I know this is the leap second list, and not the time-nuts list, but how on earth do you get a good, stable frequency to tick to if you have the base frequency provided by the carrier of the signal, but need to do phase offsets to keep it in sync (which means frequency skews to steer them in/out).  The data is only good to 100ms, so you'd see a lot of jumps you'd have to smooth out.  And what's the right time constant for steering, etc


I was only ever involved in management-plane systems, where the main issue is making sure that the billing periods are aligned with legal time.  100ms jumps here and there don't matter for that, unless they happen to occur at the boundaries between rates.

ian